A former Lehman Brothers trader has filed a $50 million lawsuit against the manager who fired him for calling a female broker the “C”-word.

Kai Kemnitz’s suit says the canning was unfair because such language is “commonplace” on Wall Street.

In papers filed in Manhattan Supreme Court, Kemnitz says Jeffrey Michaels convinced him to leave his lucrative and secure job at Deutsche Bank for a $2.7 million-a-year gig at Lehman – and then booted him for a one-time dropping of the “C”-bomb.

Kemnitz admitted using the foul word for female genitalia, but maintained that “its use was simply no basis for termination” because bad language is “frighteningly common” on Wall Street.

“During this period and other periods of intense trading, foul language and aggressive behavior were commonplace on Lehman’s trading floor, on other trading floors, and in the market in general,” the suit says.

Kemnitz filed a similar action in federal court against Lehman earlier this year, but it was put on ice after the firm collapsed last month and filed for bankruptcy.

The suit says Kemnitz was raking in a seven-figure salary at Deutsche Bank when Michaels wooed him to Lehman in November 2006. In addition to promising a $2.7 million salary, Michaels told the German national he’d have assistance obtaining a green card, the filing says.

He had the run-in on the phone with a female broker who he said cost him a big deal, the suit says. Michaels heard the exchange and fired him. Michaels, who’s since left Lehman, did not return a call for comment.